This article describes several alternative processes for adding crawl space insulation and the use of spray foam insulation in crawl areas. We include photos that compare spray foam insulation with cut-and-paste foam board insulation.

Our page top photo shows why you would want to remove old fiberglass insulation, then clean, and properly insulate an existing crawl area, but the advice below pertains to new construction as well.

Crawl Area Insulation Retrofits - OK to use Spray Foam

At ICYNENE FOAM SPRAY INSULATION we discussed the properties of Icynene® foam insulation (and similar products). This foam is a spray-in-place product, injected through openings, or pour-in expanding-foam insulation product. Other water borne foam spray insulation products, including some latex-foams, are available.

Our photo (left) illustrates the author testing for air leaks at an apparent void in foam insulation sprayed in a tight crawl space.

Where access is very restricted it can be difficult to spray any foam in a smooth, uniform, and airtight pattern. Our next photo (below left) illustrates a mixed-media insulation retrofit in a crawl area.

At URETHANE FOAM Deterioration, Outgassing we discussed some historic concerns surrounding polyurethane foam insulation, including the water resistance of open-celled spray foams, outgassing, and insect resistance.

But there are modern spray polyurethane products that are closed-cell insulation suitable for use in damp locations and that may perform well in a crawl space, avoiding the issues we discussed above as well as the issue of mold formation in fiberglass insulation.

Here is what the U.S. Department of Energy says about polyurethane insulation in buildings - (the US DOE comments are consistent with our text above):

Polyurethane is a closed-cell foam insulation material that contains a low-conductivity gas (usually hydrochlorofluorocarbons or HCFC) in its cells. The high thermal resistance of the gas gives polyurethane insulation materials an R-value typically around R-7 to R-8 per inch.

Over time, the R-value of polyurethane insulation can drop as some of the low-conductivity gas escapes and air replaces it. This phenomenon is known as thermal drift. Experimental data indicates that most thermal drift occurs within the first two years after the insulation material is manufactured. The R-value then slowly decreases. For example, if the insulation has an initial R-value of R-9 per inch, it will probably eventually drop to R-7 per inch. The R-value then remains unchanged unless the foam is damaged.

Polyurethane insulation is available as a liquid sprayed foam and rigid foam board. It can also be made into laminated insulation panels with a variety of facings.

Sprayed-Foam Polyurethane Insulation

Sprayed or foamed-in-place applications of polyurethane insulation are usually cheaper than installing foam boards. These applications also usually perform better since the liquid foam molds itself to all of the surfaces.

All closed-cell polyurethane foam insulation made today is produced with a non-CFC (chlorofluorocarbon) gas as the foaming agent. Some polyurethane foam combines with a HCFC gas. These types don't insulate as well as insulation made with a CFC gas, but the non-CFC gas is less destructive to the ozone layer. However, these foams still have an aged R-6.5 per inch thickness. Their density is generally 2.0 lb/ft3 (32.0 kilograms per cubic meter [kg/m3]). There also are low-density open-cell polyurethane foams (0.5 lb/ft3 [8 kg/m3]). These foams are similar to conventional polyurethane foams, but are more flexible. Some low-density varieties use carbon dioxide (CO2) as the foaming agent.

Low-density foams are sprayed into open wall cavities and rapidly expand to seal and fill the cavity. One manufacturer offers a slow-expanding foam, which is intended for cavities in existing homes. The liquid foam expands very slowly and thus reduces the chance of damaging the wall from overexpansion. The foam is water-vapor permeable, remains flexible, and is resistant to wicking of moisture. It provides good air sealing and yields about R-3.6 per inch of thickness. It is also fire resistant and won't sustain a flame.

Soy-based, polyurethane liquid spray-foam products are also available. The cured R-value is around 3.7 per inch. These products can be applied with the same equipment used for petroleum-based polyurethane foam products.

Insect Attack on Foam Insulated Foundations

Wood destroying insect effects of foam insulation: foam insulation is not an insect barrier; while these materials do not provide food for termites, they are easily penetrated by termites or carpenter ants (as are other insulating materials). For this reason our opinion is that it is bad design to bring foundation insulating foam panels up into contact with building wood framing materials unless an approved insect barrier has also been installed.

What can we do to improve the insect resistance of buildings where solid foam board or foam spray foundation insulation are being applied? Having read our recommendations and warnings at Insects & Foam Insulation, reader S. Frank asked if insulating a crawl space with spray foam would create a risk of insect attack on the building.

The insect path formed by foam, such as foam board on the outside of a foundation and brought up in contact with wood framing, can be a risk to a building, especially if wood destroying insects are common in the area and if other factors such as water conducive to insect attack are present. Insects don't "eat" the foam but it can provide a protected pathway up from soil into wood structural elements.

If the spray foam application in a crawl space does not make a connection from soil up to wood, you may have avoided that concern. Six to eight inches of clear exposed masonry foundation between the soil and the bottom of insulating material will discourage insect attack and will also permit inspection for evidence of termites or other wood destroying insects.

BASEMENT HEAT LOSS discusses the percentages of heat loss with different basement or crawl area insulation schemes. You may find that there is comparatively little energy savings lost by leaving the bottom few inches of the foundation wall exposed in the crawl area.

If the building is not in an area where wood destroying insect damage is common, that concern may not pertain.

If the crawl space is being kept dry you will reduce the chances of an insect attack through the crawl space interior -
see CRAWL SPACE DRYOUT - home

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Technical Reviewers & References

Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com

John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net

The Home Reference Book, a reference & inspection report product for building owners & inspectors.Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Asbestos: How to find and recognize asbestos in Buildings - visual inspection methods, list of common asbestos-containing materials

Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on Asbestos, Its Industrial Applications, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print).

Asbestos Identification and Testing References

Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
the basis for current work by asbestos identification laboratories.

Brick Nogging, Historical Investigation and Contemporary Repair, Construction Specifier, April 2006. Historical use of brick in timber-framed buildings, drawing on the investigations of the Kent Tavern in Calais, VT.
"Brick nogging is a European method of construction which was brought to the new world in the early-nineteenth century. It was a common construction method that employed masonry as infill between the vertical uprights of wood framing." -- quoting the web article review.

Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.

How could homes be designed and built more efficiently?

What kinds of construction and production techniques worked well and which did not?

How did people use different kinds of spaces in their homes?

What roles did community planning, zoning, and interior design play in how neighborhoods worked

Rubblestone Wall Filler: See this Lartigue House using exterior-exposed rubblestone filler between vertical timbers of a post and beam-framed Canadian building.

Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.